1. Field of the Invention
This invention relates to an optical scanner, and more specifically, to a magnification-variable optical scanner in which two-stage, multi-stage or continuous variation is available.
2. Description of Related Art
The demand for multimedia information has become remarkable with the recent development of information technology. Therefore, pictures are required in some documents which in the past were text-only documents. In order to satisfy the demand for large amounts of image data, a picture catcher is generally utilized as a data input device. The optical scanner has recently become one of the foremost picture catchers because of its performance and price. However, the scan quality of the optical scanner has some limitations. The resolution, which is requested at first when an optical scanner is considered, is determined by an image detector therein. In general, the image detector is a charge-coupled device (CCD).
When the object surface of a specific area is scanned, a CCD device with a sufficient number of pixels is required to satisfy the resolution requirement. Therefore, more CCD pixels are necessary for a higher scan resolution. However, more CCD pixels result in higher costs and longer scanning time. The resolution can also be improved by changing the magnification. But although the scanning time is unchanged, the scanned area is reduced, that is, the object surface becomes smaller. However, in view of costs, most conventional systems change the magnification to improve the resolution from, for example, 600 dpi to 1200 dpi.
The magnification of a conventional optical system is modified, in general, by a zoom lens. The zoom lens is difficult to design and has a very complicated structure. Therefore the optical system has difficulties in modifying its magnification by the zoom lens, and manufacturing costs are higher.